In many automotive lighting and display applications it is desirable to have a light fixture providing collimated, uniform intensity light emission over a large areal extent, in fixtures of minimal thickness. The thickness or depth of the light source is of particular importance in the field of automotive lighting because volume enclosed by the light fixture is lost to passenger or cargo space. The typical method of providing collimated beams of light is to utilize parabolic reflectors. Two disadvantages exist in the use of parabolic reflectors, however. One disadvantage relates to the size of the parabolic reflector. If the light source is to have a large aperture, the parabolic reflector must be relatively deep. This is incompatible with the goal of minimum thickness designs.
A second disadvantage lies in the existence of "hot" spots in the parabolic reflector's light emission pattern. The non-uniform emission results because the parabolic reflector is more efficient at gathering light near the center than at the edges.
Many light fixture designs have elongated light-emitting sections and may have a plurality of such regions. Such fixtures generally utilize multiple parabolic reflectors and light sources, requiring additional wiring and maintenance. Furthermore a parabolic reflector produces only a single collimated beam of light from a light source. Thus to illuminate multiple region, multiple light sources and reflectors are required even if the illuminated regions are small.
Reflective Fresnel structures that offer reductions in the depth requirements of parabolic reflectors are taught in U.S. Pat. No. 4,789,921, commonly assigned herewith. While reducing the volume enclosed by the light fixture, these devices do not provide a uniform intensity over the entire light-emitting surface.
Another approach to providing uniform intensity light emission over an extended area is taught in U.S. Pat. No. 4,799,137, commonly assigned herewith. The approach of that patent uses an optical cavity containing a substantially perpendicularly light reflecting film. A collimated light source provides light which is nearly parallel to the surface of the reflective film, resulting in reflected light emission substantially perpendicular to an optical window. That approach allows the fixture to be of shallow depth, while providing substantially uniform, collimated light emission over an extended area. It does not, however, adequately solve the problem of allowing a single light source to provide uniform intensity, collimated light emission from a light fixture with multiple elongated light-emitting regions which have a common junction.